During his time as responsible of the financial department of Union Allied Construction, McClintock used the company to transfer money for Wilson Fisk, the leader of the company. Karen Page, the secretary to the chief accountant, opened a file showing these money transfers, covered as company pension. Not knowing what to do with the file she went to visit McClintock to tell him about the file. McClintock laughed it off and told Page the file was a theoretical model that they were screwing around with.
Not trusting the story she was given by McClintock, the story eventually went to the press. With the story out to the public Union Allied Construction fell. To make sure McClintock would not talk to the press, he was killed by Fisk's men, making it look like he overdosed.
When Fisk ordered James Wesley to get John Healy killed, Wesley told him that with the murders they commited lately, including the one on McClintock, they are leaving a trail of bodies that would eventually lead somewhere.
Since the fall of Union Allied Construction and the murder of Daniel Fisher, Page was determined to expose a criminal empire working in Hell's Kitchen. One of the people she tried to have on her case was Ben Urich, investigative journalist at the New York Bulletin. During one of their meetings, Urich told Page that her old boss McClintock "overdosed on pills, or some such." 
- Karen Page - Former Employee